1. Field of the Invention
This invention relates to sensors. In particular, there is a sensor that can measure the relative displacement between two rotating shafts. The sensor can be used to sense the amount of torque applied to a steering wheel in vehicle.
2. Description of the Related Art
Various devices and methods of dealing with the design of steering wheel sensors are known. Examples of patents related to the present invention are as follows, and each patent is herein incorporated by reference for the supporting teachings:
U.S. Pat. No. 5,353,004 is a sensor for detecting steering angle.
U.S. Pat. No. 5,818,038 is a steering wheel angular position sensor.
U.S. Pat. No. 5,434,784 is a vehicle steering wheel position sensing apparatus.
U.S. Pat. No. 5,248,939 is an apparatus for sensing the direction and speed of a steering wheel shaft using hall effect sensors in a detachable sensor mounting.
U.S. Pat. No. 5,044,084 is an angle sensor element.
U.S. Pat. No. 4,839,579 is a resistive steering sensor.
U.S. Pat. No. 5,309,758 is a steering angle sensor for automobile.
U.S. Pat. No. 4,955,228 is a device for detecting rotation of steering wheel for automobiles.
U.S. Pat. No. 5,238,076 is an electric power steering for parking.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicants"" acknowledged duty of candor in disclosing information that may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, the applicant""s claimed invention.
3 Problem with the Related Art
There are several problems occurring with the prior art. The prior art steering wheel sensors have sensed rotational position of the wheel. In particular, U.S. Pat. No. 5,353,004 discloses a device that mounts on the end of a steering wheel that measures two parameters. First, it measures where on a 360 degree turn the steering wheel is positioned. Second, it measures which turn the steering wheel is on. Typically, the steering wheel is rotated four turns, to turn the front wheels all the way from the left most position to the right most position. We will call the left most turn, turn 1 and the right most turn, turn four. The middle or straight position would be between turns 2 and 3. In other words, the wheel would have to rotate through 1440 degrees of rotation to complete four turns. The device of U.S. Pat. No. 5,353,004 does not measure torque applied between the steering wheel and the steering linkage.
More recently, efforts by the automotive industry have been focusing on electrical assist power steering for vehicles. The electrical assist power steering unit is an electrical motor attached to the steering linkage that operates when assist is required. A large amount of torque on the steering wheel occurs at low speed operation or during parking. The electrical assist power steering is generally not needed during high speed operation such as during highway driving. The major advantages of electrical assist power steering are first, that it only operates during the short time of turning and is inoperative the rest of the time and second that it is simpler to manufacture. In a hydraulic power steering system, the power steering pump is always being turned by the engine and represents an energy drain on the motor all the time even though steering is only performed during a small percentage of the total time a car is operated. An electrical assist power steering system requires sensing of torque applied to the steering wheel. The torque indicates how much force the operator is exerting to move the wheel. The output signal from a torque sensor is fed into a control unit which controls the electrical motor of the assist unit. When the torque sensed is high, the assist applied to the steering linkage will be high. When the torque sensed is low, the assist applied to the steering linkage will be low. Unfortunately, the current electrical assist power steering units tend to overshoot or overcompensate once it is activated. The operator will tend to have to counter compensate a small amount with the wheel during operation so that the wheel does not turn beyond the desired turning point. It is desirable to provide an advanced electrical assist power steering system with better operator ergonomics that feels the same during operation as the current hydraulic power steering systems. In order to accomplish this, the control unit needs precise torque information. With a precise torque sensor, the control unit can operate in various modes. For example, when the steering wheel rotation is reversed, the rotational position sensor can sense the reversal and the electric motor can be reversed before a large reverse torque is built up on the wheel and felt by the operator. This faster motor reversal leads to better operator ergonomics.
In general, a sensor that measures the relative displacement between two rotating shafts has useful applications in the areas of industrial machinery, aerospace, electrical power generation and transportation.
There is a current unmet need for precise steering wheel torque sensor that is readily manufacturable at low cost. Additionally, there is a current unmet need for a sensor to measure the relative displacement between two rotating shafts.
It is a feature of the invention to provide a sensor to measure the relative displacement between two rotating shafts.
It is a feature of the invention to provide a steering wheel sensor that can sense a torque applied to the steering wheel of a vehicle.
Yet, another feature of the invention is to provide a sensor for attachment between a first and second rotating shaft for measuring the relative displacement between the first and second rotating shafts. The sensor includes a housing that has apertures at each end. The first and second shafts pass into the housing. A sensor assembly is located in the housing and is connected to the first and second shafts to sense the relative rotational displacement of the first and second shafts. The sensor assembly generates an electrical signal. An electrical connector is located in the housing and electrically connects with the sensor assembly to provide the electrical signal to an external electrical circuit. The sensor assembly has a planetary gear assembly that is connected to the first and second shafts. A variable magnetic field generator is connected to the planetary gear assembly. The variable magnetic field generator moves proportional to the relative rotational displacement of the first and second shafts. A magnetic field sensor is located adjacent the variable magnetic field generator and is connected to the electrical connector for generating the electrical signal in response to rotational movement of the variable magnetic field generator. The planetary gear assembly has a housing and an upper carrier that is connected to the first shaft. A lower carrier is connected to the second shaft and is located adjacent the upper carrier. The upper and lower carriers are located within the housing. An upper set of planet gears is located on and rotatably supported by the upper carrier. A lower set of planet gears is located on and rotatably supported by the lower carrier. A sun gear is located within the upper and lower carriers between the upper and lower gears. The sun gear engages the upper and lower planet gears. An upper ring gear surrounds and engages the upper set of planet gears. A lower ring gear is attached to the housing. The lower ring gear surrounds and engages the planet gears. The upper ring gear moves proportional to the relative rotational displacement of the first and second shafts. The variable magnetic field generator has a tapered magnet that is located in a section of the upper ring gear. An aperture is located in the tapered magnet. The magnetic field sensor is located in the aperture. The magnetic field sensor is a hall effect sensor. The first shaft can be connected to a steering wheel and the second shaft can be connected to a vehicle steering linkage. The sensor is then operable to measure a torque applied to the steering wheel.
The invention resides not in any one of these features per se, but rather in the particular combination of all of them herein disclosed and claimed. Those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Further, the abstract is neither intended to define the invention of the application, which is measured by the claims, neither is it intended to be limiting as to the scope of the invention in any way.